Derivatives and Hedging Activites (Option Pay/Rec) (Details 3) $ in Millions	Jun. 30, 2018 USD ($)
Summary of Option Premiums Payable and Receivable
Premiums payable	$ 1,589
Premiums receivable	720
2018 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	104	[1]
Premiums receivable	37	[1]
2019 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	295
Premiums receivable	172
2020 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	217
Premiums receivable	132
2021 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	187
Premiums receivable	120
2022 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	250
Premiums receivable	200
2023-2027 [Member]
Summary of Option Premiums Payable and Receivable
Premiums payable	536
Premiums receivable	$ 59

[1] 2018 amounts represent the amounts payable and receivable for the period from July 1, 2018 to December 31, 2018.